In the manufacture of tiles as an inorganic fired article, for example, the tiles are conventionally colored as follows. A coloration agent (colorant) containing metal oxide powder as a basic raw material is admixed with a clay raw material to form a color developing clay (color clay), which is fired to accomplish the coloration.
The coloration agent generally contains, as the basic raw material, at least one selected from the group consisting of ferric oxide (Fe2O3), copper oxide (Cu2O) manganese oxide (MnO), chromium oxide (CrO), cobalt oxide (CoO), vanadium oxide (VO) and the like. The coloration agent is capable of coloring the tiles in a particular color according to the compositions thereof.
The metal oxide powder as the basic raw material of the coloration agent is generally produced as follows. A metal as a raw material is wet milled to a suitable particle size. The resultant particles are calcined. Subsequently, the particles are wet milled again and then, are dry milled to form fine powder.
On the other hand, shot waste produced as a by-product of shot blasting metal normally contains spent shots (steel balls) and metal powder. Unfortunately, the metal powder is prone to scatter so that the shot waste suffers difficult handlings such as transportation and storage. Shot waste containing iron-based metal powder, in particular, is prone to ignition. This leads to an even more difficult handling of such shot waste. In addition, the reuse of such shot waste is disadvantageous in technical and cost terms. In actual condition, therefore, the above shot waste is disposed of in landfill sites as industrial waste.
The metal oxide powder as the basic raw material of the coloration agent requires repeated steps of grinding the metal by means of a mill. Therefore, the manufacture of the powder takes a large number of steps, resulting in a high manufacture cost.
What is more, the aforesaid landfill disposal of the shot waste is undesirable from the viewpoint of effective use of resources. There are also other problems of environmental deterioration and high disposal costs.
In view of the foregoing problems, the invention has been accomplished and has an object to provide a coloration agent for use in ceramic articles which offers an effective reuse of the shot waste and which contributes to the reduction of manufacture costs, as well as to provide a color developing clay using the same.